| Title of Invention | PROCESS WINDOW FOR PRODUCTION OF HOT ROLLED GALVANIZED STEEL SHEETS |
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| Abstract | According to the invention, there is provided a process window for production of hot rolled galvanized steel sheets comprising the steps of:-(i)Cleaning of steel sheets by pickling with acid such as Hcl for removing the oxides present on the surface of said sheets; (ii)Soaking the steel sheets in continuous annealing furnace, heated @20°C /sec at a soaking temperature of 750°-800°C for 90-100 sec, maintaining a line speed @ 40-60 mpm and having reducing atmosphere to achieve complete re-crystallised microstructure; (iii) Reducing there after the temperature @20°C per sec to 460°-480°C equivalent to zinc bath temperature and (iv) Cooling the steel sheet, after recrystallation annealing, in zinc bath maintained at 460-480° for 5-7 seconds for proper galvanization. |
| Full Text | FIELD OF THE INVENTION The present invention relates to an improved galvanizing process of hot rolled steel sheets for optimizing process window to yield spot less surfece. BACKGROUND OF THE INVENTION HR steel sheets have shown significant amount of alloying element segregation and these affect of zinc coatability on the steel surfece. It is observed that for low carbon steels in comparison to other alloying elements, carbon gets easily segregated at the surface as carbide. Depending on the processing condition of the hot rolled steel production different alloying elements also get segregated at the surface level. So in order to achieve proper galvanizing the determination of optimized process window is necessary. The present innovation is a technique to get proper galvanizing of the hot rolled steel sheets. OBJECTS OF THE INVENTION It is therefore, an object of the present invention to propose an improved galvanizing process of hot rolled steel sheet which yield spot less steel surfece. Another object of the present invention is to propose an improved galvanizing process of hot rolled steel sheet which improve Zn-Coatability of the hot rolled low carbon Aluminum killed sheets. A further object of the present invention is to propose an improved galvanizing process of hot rolled steel sheets which increases the corrosion properties. A still further object of the present invention is to propose an improved galvanizing process of hot rolled steel sheets which increases the formability properties. SUMMARY OF INVENTION According to the invention, there is provided a process window for production of hot rolled galvanized steel sheets comprising the steps of:-(i) Cleaning of steel sheets by pickling with acid such as Hcl for removing the oxides present on the surface of said sheets; (ii)Soaking the steel sheets in continuous annealing furnace, heated @20°C /sec at a soaking temperature of 750°-800°C for 90-100 sec, maintaining a line speed @ 40-60 mpm and having reducing atmosphere to achieve complete re-crystallised microstructure; (iii) Reducing there after the temperature @20°C per sec to 460°-480°C equivalent to zinc bath temperature and (iv) Cooling the steel sheet, after recrystallation annealing in zinc bath maintained at 460-480° for 5-7 seconds for proper galvanization. BRIEF DESCRIPTION OF THE ACCOMPAYING DRAWINGS Fig 1- Schematic diagram of the process window of the galvanizing Fig 2- A photographic view of LCA1 hot rolled galvanized steel sheets. Fig 3- Total corrosion data of LCAL rolled galvanized in comparison with cold rolled galvanized. Fig 4-A photographic view of bend hot rolled galvanized steel sheet Fig 5- Micro structure of the bend portion showing no cracks in galvanized_portion DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION The HR steel sheet used for the experimentation is LCAK steel whose composition given in Table 1. Before doing any galvanizing operation the samples were pickled with acid to remove the oxide present at the surface of steel sheets. This pickling operation removes all the oxides formed during the hot rolling operations but unable to remove segregated alloying elements. To galvanize this steel one galvanizing process cycle is employed which is shown schematically in Fig 1. The condition maintained In Continuous annealing furnace: 1. Atmosphere: N2-20% H2 2. Dew point:-35°C to-40°C 3. Soaking temperature: 750-800°C. 4. Holding time inside the furnace: 90 sec-100 Sec 5. Line speed :40-60 mpm. The Condition maintained In galvanizing bath: 1. Bath composition : Zn-0.2% Al 2. Bath temperature: 460°C-480°C 3. Dipping time 5 sec-7 sec. The result of the galvanizing operation on steel surface is shown in fig 2, From Fig 2 marked area which can be considered as proper galvanizing area has shown complete coating without any bare spot. The corrosion behavior of the above mentioned steel sheets has been compared with cold rolled galvanized steel sheets in fig 3. The corrosion data for both the steel sheets are given in Table 2. From table 2 it can be concluded that newly produced hot rolled galvanized steel sheets have similar corrosion properties of cold rolled one. In order to know the fbrmability properties the hot rolled galvanized steel sheet is bent up to 180° in hydraulic press as shown in fig 4. Bent sample has shown no coating de-lamination and the microstructure of the bent portion is shown in fig 5. From the microstructure it is evident the no coating cracks or de-lamination has been observed. Therefore, the newly produced hot rolled galvanized steel sheets are having similar properties like cold rolled galvanized steels. WE CLAIM; 1. A process window for production of hot rolled galvanized steel sheets comprising the steps of:- (i) Cleaning of steel sheets by pickling with acid such as Hcl for removing the oxides present on the surface of said sheets; (ii) Soaking the steel sheets in continuous annealing furnace, heated @20°C /sec at a soaking temperature of 750°-800°C for 90-100 sec, maintaining a line speed @ 40-60 mpm and having reducing atmosphere to achieve complete re-crystallised microstructure; (iii) Reducing there after the temperature @20°C per sec to 460°-480°C equivalent to zinc bath temperature; (iv)Cooling the steel sheet, after recrystallation annealing in zinc bath maintained at 460-480° for 5-7 seconds for proper galvanization. 2. A process window as claimed in claim 1 wherein in the reducing atmosphere content inside the annealing furnace is N2-20% H2. 3. The process window as claimed in claim 1 wherein the said annealing furnace provided a dew point-35°C to -40°C. 4. The process window as claimed in claim 1 wherein the said Zn bath content is Zn-0.2%A1. 5. The process window as claimed in claim 1 wherein the duration for steel sheets dipping in Zn- bath is 5 sec to 7 sec. ABSTARCT PROCESS WINDOW FOR PRODUCTION OF HOT ROLLED GALVANIZED STEEL SHEETS According to the invention, there is provided a process window for production of hot rolled galvanized steel sheets comprising the steps of:-(i)Cleaning of steel sheets by pickling with acid such as Hcl for removing the oxides present on the surface of said sheets; (ii)Soaking the steel sheets in continuous annealing furnace, heated @20°C /sec at a soaking temperature of 750°-800°C for 90-100 sec, maintaining a line speed @ 40-60 mpm and having reducing atmosphere to achieve complete re-crystallised microstructure; (iii) Reducing there after the temperature @20°C per sec to 460°-480°C equivalent to zinc bath temperature and (iv) Cooling the steel sheet, after recrystallation annealing, in zinc bath maintained at 460-480° for 5-7 seconds for proper galvanization. |
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00524-kol-2008-correspondence others.pdf
00524-kol-2008-description complete.pdf
524-KOL-2008-(03-02-2012)-CORRESPONDENCE.pdf
524-KOL-2008-(03-02-2012)-FORM 1.pdf
524-KOL-2008-(13-07-2012)-CORRESPONDENCE.pdf
524-KOL-2008-(19-01-2012)- CLAIMS.PDF
524-KOL-2008-(19-01-2012)-ABSTRACT.pdf
524-KOL-2008-(19-01-2012)-DESCRIPTION (COMPLETE).pdf
524-KOL-2008-(19-01-2012)-DRAWINGS.pdf
524-KOL-2008-(19-01-2012)-EXAMINATION REPORT REPLY RECIEVED.pdf
524-KOL-2008-(19-01-2012)-FORM 1.pdf
524-KOL-2008-(19-01-2012)-FORM 2.pdf
524-KOL-2008-(19-01-2012)-FORM 3.pdf
524-KOL-2008-(19-01-2012)-OTHERS.pdf
524-KOL-2008-(19-01-2012)-PETITION UNDER RULE 137.pdf
524-KOL-2008-CORRESPONDENCE.pdf
524-KOL-2008-EXAMINATION REPORT.pdf
524-KOL-2008-GRANTED-ABSTRACT.pdf
524-KOL-2008-GRANTED-CLAIMS.pdf
524-KOL-2008-GRANTED-DESCRIPTION (COMPLETE).pdf
524-KOL-2008-GRANTED-DRAWINGS.pdf
524-KOL-2008-GRANTED-FORM 1.pdf
524-KOL-2008-GRANTED-FORM 2.pdf
524-KOL-2008-GRANTED-SPECIFICATION.pdf
524-KOL-2008-REPLY TO EXAMINATION REPORT.pdf
| Patent Number | 253772 | |||||||||
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| Indian Patent Application Number | 524/KOL/2008 | |||||||||
| PG Journal Number | 34/2012 | |||||||||
| Publication Date | 24-Aug-2012 | |||||||||
| Grant Date | 23-Aug-2012 | |||||||||
| Date of Filing | 14-Mar-2008 | |||||||||
| Name of Patentee | TATA STEEL LIMITED | |||||||||
| Applicant Address | RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION, JAMSHEDPUR | |||||||||
Inventors:
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| PCT International Classification Number | C23C2/06 | |||||||||
| PCT International Application Number | N/A | |||||||||
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